1. Technical Field
The present invention relates to an electro-optical device suitable for display of various kinds of information.
2. Related Art
In a known electro-optical device, for example, in a liquid crystal device, a driver (hereinafter, simply referred to as an ‘LCD driver’) for driving a liquid crystal panel is connected with a flexible substrate (FPC: flexible printed circuit) and the flexible substrate is connected with an external electronic apparatus through a connector. A voltage is supplied to the LCD driver from a battery provided in the external electronic apparatus. A withstand voltage of an input voltage of the LCD driver is lower than a supply voltage supplied from a battery. Accordingly, in practice, the supply voltage from the battery is converted into a voltage adapted for the LCD driver by a regulator in the external electronic apparatus before the supply voltage from the battery is supplied to the LCD driver. After receiving the supply voltage from the battery through the regulator, the LCD driver amplifies the supply voltage to a voltage suitable for image display and then supplies the amplified voltage to the liquid crystal panel.
For example, JP-A-2004-81369 discloses a technique in which before changing an output voltage of a battery to a predetermined voltage by a regulator, the output voltage of the battery is boosted by a boosting circuit only when a voltage of the battery does not reach a predetermined voltage or more and the output voltage of the battery is not boosted by the voltage boosting circuit when the voltage of the battery reaches the predetermined voltage, thereby improving the power efficiency of the battery. Furthermore, JP-A-2004-260931 discloses a technique in which a voltage input to a backlight driving circuit is supplied directly from a battery during an operation period for which an output voltage of the battery is equal to or larger than a predetermined value and the voltage input to the backlight driving circuit is supplied through a regulator from a point of time at which the output voltage of the battery drops to a predetermined value or less, and accordingly, the use efficiency of the battery is improved and a value close to a discharge start voltage is maintained even if a drop in the output voltage of the battery increases.
However, in the case of the LCD driver, a voltage enough not to have an influence on image display may be supplied to a liquid crystal panel by changing a voltage gain according to an input voltage. Therefore, in the case when a voltage gain is relatively high, it may be inefficient to supply the same voltage from a battery to an LCD driver all the time in terms of power consumption. However, if a voltage input to an LCD driver is set to be low, image display may be adversely affected when the voltage gain is relatively low. Examinations on these points are not made in JP-A-2004-81369 and JP-A-2004-260931.